1. Field of the Invention
The present invention relates to printing apparatuses.
2. Description of the Related Art
Printers for printing and recording data at a high resolution are used for multimedia processing in fields such as computer aided design (CAD), computer graphics (CG), design and business desktop publishing (DTP) and are now commercially available.
Such a printer receives page-description-language (PDL) data sent from a host computer, analyzes it, creates the corresponding intermediate-language data, holds one page of that data, and renders (rasterizes) the held intermediate-language data at a high speed using hardware and/or software.
Intermediate-language data can be handled at high speed even if hardware is used. It includes a run-length object which has a set of the coordinates of the rightmost and leftmost points in the longitudinal direction in an object and an image object which includes image data as is.
Form overlay printing means that the same form data, such as a line and a logo, is repeatedly printed without frequently sending the data from the host computer, by storing the form data in a file system in the printer as intermediate-language data, and specifying the stored data when the form is drawn on a plurality of pages.
Form overlay printing can be implemented by three PDL commands, a form-registration start command, a form-registration end command and a form designation command. PDL data disposed between the form-registration start command and the form-registration end command is converted to the intermediate-language data, is assigned a unique name, and is registered in a file system of the printer as form data.
Intermediate-language data is created by manipulating PDL data such that the image data corresponding to the PDL data is readily created.
When a form designation command is detected in PDL data, the form data (intermediate-language data) having the specified name is copied to a memory space in which other intermediate-language data is stored, analyzed, converted to the image data and stored in a page buffer.
Since a form designation command can be called many times, a page having the same format can be repeatedly rendered (rasterized) by calling the command at different pages.
Some recently available printers receive PDL data sent from the host computer, analyze it, create the corresponding intermediate-language data, hold one page thereof, and perform rendering (rasterization) of the intermediate-language data at high speed by hardware or software with the alternate use of two band memory units when paper is discharged.
A simple intermediate language can be used at high speed even if hardware is used. It includes a run-length intermediate language which has a set of the coordinates of the rightmost and leftmost points in the longitudinal direction in an object, an image intermediate language which includes image data as is and a compressed image intermediate language which includes compressed images. Some image intermediate languages handle multiple-valued images having two, four, or eight bits per pixel, and draw images at the gray-scale levels of the printer according to positions where images are drawn.
Some intermediate languages create inverted black-and-white characters by applying a logical drawing method to the destination image already rendered (rasterized) on memory when intermediate-language data is rendered (rasterized).
Such a conventional printing apparatus has the following problems.
Since intermediate-language data is analyzed each time a form designation command is called, the data is analyzed at the same time rasterizing is performed, resulting in a long processing time. Although the size of intermediate-language data is generally smaller than that of the corresponding PDL data, the corresponding rendered (rasterized) data may be smaller when images are drawn at the same position.
Multiple-valued intermediate-language data is larger in size than two-valued-image intermediate-language data. When a plurality of intermediate-language data items are drawn at the same position, the size of an intermediate-language storage area needs to be very large.
When a number of intermediate-language data items are drawn in the same band, or there is a plurality of intermediate-language data items which require a long rasterization time, the development speed for intermediate-language data may be slower than the printer engine speed.
In the cases described above, degraded image data is created with lower resolution or a lower number of gray-scale levels, a memory area of one page for storing the image data is obtained, all intermediate-language data items are developed on that page, and paper discharge processing is performed. The output of the printer may become degraded depending on the data.